Outer sole and shoe

ABSTRACT

An outer sole of the present invention includes a thermoplastic elastomer and has a surface free energy of 12 mJ/m 2  or higher. Such an outer sole has an excellent grip performance on a road surface and is suitable for a component of a shoe.

TECHNICAL FIELD

The present invention relates to an outer sole of a shoe and a shoe having the same.

BACKGROUND ART

Various shoes including sports shoes are composed of a shoe body and an outer sole attached to the bottom side of the shoe body.

Typical shoes are required to have a grip performance on a road surface. The term “grip performance” herein refers to the slip resistance. The term “road surface” herein refers to any surface on which a person wearing shoes walks or runs, including the surface of a road such as a sidewalk, the surface of a floor in a building such as a gymnasium, and the surface of unpaved ground. By improving the grip performance of an outer sole, which is a component of a shoe that comes into contact with a road surface, the slip resistance of the shoe can be improved.

Conventionally known outer soles with the improved grip performance include an outer sole produced by using a polymer material having a relatively high glass transition temperature and an outer sole produced by using a short fiber (Patent Document 1).

However, the level of grip performance exhibited by conventional outer soles is not high enough. The level of grip performance exhibited by conventional outer soles on a wet road surface, in particular, is not enough due to the presence of liquid between the wet road surface and the outer sole surface. The term “outer sole surface” herein refers to one of the surfaces of an outer sole that comes into contact with a road surface. The term “liquid” herein refers to water or oil, for example, present on a road surface.

PATENT DOCUMENT

[Patent Document 1] JP 2009-249457 A

SUMMARY OF THE INVENTION Technical Problem

An object of the present invention is to provide an outer sole having an excellent grip performance and a shoe having the same.

Solution to Problem

The outer sole of the present invention includes a thermoplastic elastomer and has a surface free energy of 12 mJ/m² or higher.

The outer sole of the present invention has an arithmetic mean roughness, Ra, of 1000 μm or lower.

In the outer sole of the present invention, the thermoplastic elastomer contains at least one elastomer selected from a chlorinated polyethylene-based elastomer, a chlorosulfonated polyethylene-based elastomer, a styrene-based elastomer, an olefin-based elastomer, a polyamide-based elastomer, and a urethane-based elastomer.

In the outer sole of the present invention, the thermoplastic elastomer contains at least one of a chlorinated polyethylene-based elastomer and a chlorosulfonated polyethylene-based elastomer.

According to another aspect of the present invention, a shoe is provided.

The shoe of the present invention includes any one of the outer sole mentioned above.

An outer sole of the present invention has an excellent grip performance, particularly on a wet road surface.

A shoe having this outer sole has a slip resistance to be exhibited during walking on a dry road surface and even on a wet road surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view illustrating a first embodiment of the shoe according to the present invention.

FIG. 2 is an enlarged sectional view of FIG. 1 taken from line II-II, with the upper portion of a shoe body omitted.

FIG. 3 is a side view illustrating a second embodiment of the shoe according to the present invention.

FIG. 4 is a graph showing the measurement results of the coefficients of static friction and the coefficients of dynamic friction of outer soles of Examples 1 to 5 and Comparative Example 1.

FIG. 5 is reference table (A) showing results of testing necessary to explain the [Preliminary findings] section.

FIG. 6 is reference table (B) showing results of testing necessary to explain the [Preliminary findings] section.

FIG. 7 is reference figure (C) showing results of friction testing that was conducted in the [Preliminary findings] section.

FIG. 8 is reference table (D) showing results of testing necessary to explain the [Preliminary findings] section.

FIG. 9 is reference figure (E) describing the spreading coefficient in the [Preliminary findings] section.

FIG. 10 is reference figure (F) describing the work of adhesion in the [Preliminary findings] section.

FIG. 11 is reference table (G) showing results of testing necessary to explain the [Preliminary findings] section.

FIG. 12 is reference table (H) showing results of testing necessary to explain the [Preliminary findings] section.

FIG. 13 is reference table (I) showing results of testing necessary to explain the [Preliminary findings] section.

FIG. 14 is reference table (J) showing results of testing necessary to explain the [Preliminary findings] section.

FIG. 15 is reference table (K) showing results of testing necessary to explain the [Preliminary findings] section.

FIG. 16 is reference table (L) showing results of testing necessary to explain the [Preliminary findings] section.

DETAILED DESCRIPTION OF THE EMBODIMENTS [Principle Underlying Solution to Problems of Present Invention]

An outer sole of the present invention is produced by using a composition containing a thermoplastic elastomer, and has a surface free energy of 12 mJ/m² or higher.

A shoe having the outer sole produced by using the thermoplastic elastomer and having a surface free energy of 12 mJ/m² or higher has an excellent grip performance, particularly on a wet road surface.

While a person is walking on a wet road surface with shoes on, liquid is typically present between the outer sole surface of each shoe and the road surface, in a form of a thin film of liquid. The presence of the film of liquid prevents the outer sole surface from coming into direct contact with the road surface, and thereby the shoe easily slips on the road surface. Hereinafter, the film of liquid present between the outer sole surface and the road surface is called a “liquid film”. The inventor of the present invention conjectured that an outer sole capable of inhibiting formation of the liquid film can readily come into direct contact with a road surface and thereby have an improved grip performance on a wet road surface. Then, the inventor of the present invention has found that an outer sole containing a thermoplastic elastomer and having a surface free energy of 12 mJ/m² or higher induces spontaneous discharge of liquid from the gap between the outer sole surface and a road surface. The outer sole having a surface free energy of 12 mJ/m² or higher readily comes into direct contact with the road surface and therefore exhibits an excellent grip performance, particularly on a wet road surface. The present invention is based on preliminary findings conducted by the inventor of the present invention. First, the preliminary findings are described below.

[Preliminary Findings]

In order to study the influence of the surface free energy on the level of friction between a rubber material and a flooring, the inventor of the present invention has conducted friction testing. In the friction testing, various floorings and lubricants with different levels of the surface free energy were tested on one type of rubber material. The “rubber material” in the [Preliminary findings] section corresponds to the outer sole in the present specification. The “flooring” in the [Preliminary findings] section corresponds to the road surface in the present specification. The “lubricant” in the [Preliminary findings] section corresponds to the liquid in the present specification.

Five types of floorings were tested: polytetrafluoroethylene (PTFE), polypropylene (PP), marble, polymethylmethacrylate (PMMA), and polyethylene terephthalate (PET). Reference table (A) in FIG. 5 shows the values of arithmetic mean roughness (surface roughness), Ra, and the root-mean-square roughness, Rq, of the rubber material and each flooring. The composite roughness, σ, was calculated by Formula (1):

σ=√{square root over (Rq _(R) ² +Rq _(S) ²)}  (1)

In Formula (1), Rq_(R) and Rq_(S) each denote the root-mean-square roughness of the rubber material and the root-mean-square roughness of a flooring, respectively. The arithmetic mean roughness, Ra, was measured with an atomic force microscope (Environmental Control Unit E-sweep, manufactured by Hitachi High-Tech Science Corporation), equipped with a cantilever, SI-DF20, manufactured by Hitachi High-Tech Science Corporation. Reference table (A) has proven that the values of composite roughness, σ, of all the floorings are similar to each other. The inventors of the present invention determined that the arithmetic mean roughness (surface roughness), Ra, has not much influence on the friction testing.

As the lubricant, water or a mixture of water and ethanol (ethanol concentration of 10 vol %, 30 vol %, and 90 vol %) were used. Reference table (B) in FIG. 6 shows the viscosity of each lubricant. As the water, ion-exchanged water purified with REP343RB manufactured by Advantec was used. As the ethanol, a Wako 1st Grade reagent manufactured by Wako Pure Chemical Industries, Ltd. was used. The value of viscosity of each lubricant was from a document (Kagaku Binran, Kiso Hen (Handbook of Chemistry, Basic Version), 2nd Revision, P. 574 (1975), published by Maruzen Publishing, Co., Ltd.).

Reference figure (C) in FIG. 7 shows an outline of a friction tester (HEIDON14 manufactured by Shinto Scientific Co., Ltd.). In the friction testing, a hemispherical crosslinked isoprene rubber having an initial modulus of elasticity of 3.28 MPa was used (the hemisphere corresponded to a half of a sphere having a diameter of 25 mm). A rubber material was brought into contact with a smooth flooring that had been thoroughly immersed in a lubricant. Then, the rubber material was linearly moved at a rate of 1.67 mm/second for 2.0 seconds or longer with a vertical load of 1.96 N being applied, while the friction force was being measured. The friction force measured when the rubber material started to slide was used to calculate the coefficient of static friction. For the time period from 1.5 seconds to 2.0 seconds after the rubber material started to move linearly, the friction force remained constant. The average value of the friction force during this time period was used to calculate the coefficient of dynamic friction. No stick-slip was observed under any of the conditions of the flooring and the lubricant. This experiment was repeated three times to calculate the average. The frequency in each experiment was 1 kHz. Each experiment was conducted in the atmosphere at a temperature ranging from 22.9° C. to 24.0° C. and a relative humidity ranging from 56% to 60%. The resistance of each flooring to dissolution in each lubricant was studied by measuring changes in mass of each flooring immersed for 10 minutes in each lubricant at 25.6° C. The rate of change in mass was lower than 0.06% for any of the combinations of the floorings and the lubricants. This result has proven that all of the floorings were practically resistant to degradation caused by either water or the mixture of water and ethanol.

Reference table (D) in FIG. 8 shows the values of the surface free energy of the rubber material, the floorings, and the lubricants. The values of the surface free energy of the rubber material and the floorings were calculated according to the Kaelble-Uy's theory, based on the contact angles against 1.0 μL of ion-exchanged water and diiodomethane (Wako 1st Grade reagent manufactured by Wako Pure Chemical Industries, Ltd.), respectively, measured 10 seconds after dropping of each liquid. The contact angle was measured with a contact angle meter (DM-510Hi manufactured by Kyowa Interface Science Co., Ltd.). The values of the surface free energy of water and diiodomethane were from a document (D. H. Kaelble, The Journal of Adhesion, 2, 2 (1970) 66.). The values of the surface free energy of the lubricants were from a document (J. R. Dann, Journal of Colloid and Interface Science, 32, 2 (1970) 302.).

Progression of wetting with each lubricant at the point of contact between three materials (namely, the rubber material, each flooring, and each lubricant) (as shown in reference figure (E) in FIG. 9) is expressed as a parameter called spreading coefficient, S. The spreading coefficient, S, is calculated by Formula (2).

S=γ _(RS)−(γ_(RL)+γ_(SL))  (2)

In Formula (2), γ_(SL), γ_(RL), and γ_(RS) each denote the interfacial free energy between a flooring and a lubricant, the interfacial free energy between the rubber material and a lubricant, and the interfacial free energy between the rubber material and a flooring, respectively. The interfacial free energy was calculated according to the Kaelble-Uy's theory, by Formula (3). The spreading coefficient, S, provides the following interpretation: the formation of a liquid film at the point of contact between the rubber material, the selected flooring, and the selected lubricant is inhibited when the spreading coefficient, S, is negative, and the formation is facilitated when the spreading coefficient, S, is positive. In Formula (3), γ_(i) and γ_(j) each denote the surface free energy of substance i and the surface free energy of substance j, respectively; γ_(ij) denotes the interfacial free energy between substance i and substance j; and γ^(d) and γ^(p) each denote the dispersion component and the polar component of the surface free energy, respectively.

The amount of work required for detaching the rubber material from contact with each flooring (as shown in reference figure (F) in FIG. 10) is expressed as a work of adhesion, W. The work of adhesion, W, is calculated by Formula (4). In Formula (4), γ_(S) and γ_(R) each denote the surface free energy of a flooring and the surface free energy of the rubber material, respectively. In general, a solid-solid interface, a solid surface, and a liquid surface are all thermodynamically unstable compared to a bulk of solid or liquid. The amount of work required for detaching the rubber material from each flooring can be obtained by calculating the work of adhesion, W.

γ_(ij)=(√{square root over (γ_(i) ^(d))}−√{square root over (γ_(j) ^(d))})²+(√{square root over (γ_(i) ^(p))}−√{square root over (γ_(j) ^(p))})²  (3)

W=γ _(R)+γ_(S)−γ_(RS)  (4)

The relationship between the surface free energy of a lubricant and either of the coefficient of static friction and the coefficient of dynamic friction of the rubber material is shown in reference figure (G) in FIG. 11. Hereinafter, a coefficient of static friction and a coefficient of dynamic friction are collectively called “coefficients of static friction and dynamic friction”. The coefficients of static friction and dynamic friction of the rubber material on each flooring tended to increase as the surface free energy of the lubricant increased. In the case in which the surface free energy of the lubricant was 51.3 mJ/m² or higher, the coefficients of static friction and dynamic friction of the rubber material on PTFE, marble, PMMA, PP, and PET tended to increase in the same order. As the surface free energy of the lubricant decreased, the variations in the coefficients of static friction and dynamic friction of the rubber material on different floorings became smaller.

The relationship between the surface free energy of each flooring and the coefficients of static friction and dynamic friction of the rubber material is shown in reference figure (H) in FIG. 12. Reference figure (H) shows that there were fluctuations in the coefficients of static friction and dynamic friction of the rubber material depending on the surface free energy of each flooring, but reference figure (H) does not show any correlation between the surface free energy of each flooring and the coefficients of static friction and dynamic friction of the rubber material.

The relationship between the interfacial free energy, γ_(RS), between the rubber material and each flooring and either of the coefficients of static friction and dynamic friction of the rubber material is shown in reference figure (I) in FIG. 13. Reference figure (I) shows that there were fluctuations in the coefficients of static friction and dynamic friction depending on the interfacial free energy, and when the interfacial free energy between the rubber material and each flooring was about 8 mJ/m² regardless of the type of the lubricant, the coefficients of static friction and dynamic friction of the rubber material reached the maximum value.

The spreading coefficient, S, is an index of tendency of a lubricant to spread on a mating material. The spreading coefficient, S, at the point of contact between the rubber material, each flooring, and a lubricant indicates the tendency of the lubricant to penetrate the interface between the rubber material and the flooring, providing the following interpretation: the formation of a liquid film at the point of contact is inhibited when the spreading coefficient, S, is negative, and the formation is facilitated when the spreading coefficient, S, is positive. The relationship between the ethanol concentration in a lubricant and the spreading coefficient is shown in reference figure (J) in FIG. 14. Reference figure (J) shows that the spreading coefficient on each flooring increased as the ethanol concentration increased. The spreading coefficient on marble flooring was always higher than those of other floorings regardless of the ethanol concentration. This phenomenon occurred because the polar component, γ^(p), of the surface free energy of marble is higher than those of other floorings.

The relationship between the spreading coefficient and either of the coefficients of static friction and dynamic friction of the rubber material is shown in reference figure (K) in FIG. 15. The coefficients of static friction and dynamic friction of the rubber material on each flooring tended to decrease as the spreading coefficient increased. The coefficients of static friction and dynamic friction of the rubber material decreased sharply when the spreading coefficient was near zero. As described above, the tendency that a liquid film is formed would probably vary depending on whether the spreading coefficient is positive or negative, namely, the formation would be inhibited when the spreading coefficient is negative and would be facilitated when the spreading coefficient is positive. At the near zero spreading coefficient, the change in the state of lubrication would have caused the sharp changes in the coefficients of static friction and dynamic friction of the rubber material. Reference figure (K) in FIG. 15 shows that the coefficients of static friction and dynamic friction at a certain spreading coefficient varied depending on the type of the flooring. These results indicate that the coefficients of static friction and dynamic friction of the rubber material vary depending on the spreading coefficient and the type of the flooring.

The interface of contact between the rubber material and a flooring has an interfacial free energy, γ_(RS), and the action of external energy causes detachment of the rubber material from contact with the flooring. The energy required for this detachment is expressed as work of adhesion, W. The relationship between the work of adhesion and either of the coefficients of static friction and dynamic friction of the rubber material is shown in reference figure (L) in FIG. 16. Reference figure (L) shows that the coefficients of static friction and dynamic friction of the rubber material on any lubricant tended to increase as the work of adhesion increased. Referring to reference figure (L) in FIG. 16, the coefficients of static friction and dynamic friction of the rubber material at a certain level of work of adhesion tended to decrease as the ethanol concentration in the lubricant increased.

From these experiments, the inventor of the present invention has found the followings: as the surface free energy increases, the work required for detaching an outer sole surface from contact with a road surface increases and thereby the coefficients of static friction and dynamic friction of the outer sole on the road surface increases; and as the surface free energy increases, removal of a liquid film from the gap between the outer sole surface and the road surface is facilitated by thermodynamics, making the outer sole readily coming into direct contact with the road surface and thereby increasing the coefficients of static friction and dynamic friction of the outer sole on the road surface. These findings indicate that by producing an outer sole using a composition having a relatively high level of surface free energy, the resulting outer sole can have high levels of coefficients of static friction and dynamic friction, namely an excellent grip performance, not only on an unwet road surface but also on a wet road surface.

[Configuration of Outer Sole of Present Invention]

Next, the outer sole of the present invention will be described in detail.

The expression “from XXX to YYY” herein refers to a range “XXX or higher and YYY or lower”.

The outer sole of the present invention is produced by using a composition containing a thermoplastic elastomer, and has a surface free energy of 12 mJ/m² or higher.

It is preferable that the surface free energy of the outer sole be 15 mJ/m² or higher, more preferably 20 mJ/m² or higher, further preferably 25 mJ/m² or higher, particularly preferably 30 mJ/m² or higher. It is preferable for the surface free energy of the outer sole to be as high as possible, with no upper limit. Practically, the upper limit to the surface free energy of the outer sole produced by using the composition containing the thermoplastic elastomer is 73 mJ/m² or lower, for example.

The surface free energy of the outer sole can be determined according to the Kaelble-Uy's theory, in the same manner as in the

[Preliminary Findings] Section.

More specifically, the value of the surface free energy of the outer sole can be determined as follows: on the outer sole surface, 1 μL of ion-exchanged water and 1 μL of diiodomethane are dropped; 10 seconds later, the contact angles of the liquid drops are measured; the values of the contact angles are substituted into the simultaneous equations of Formulae (x1) and (x2); and the solutions, γ^(d) and γ^(p), are substituted into Formula (y).

As the diiodomethane, a Wako 1st Grade reagent manufactured by Wako Pure Chemical Industries, Ltd. may be used. As the device for contact angle measurement, a contact angle meter (DM-510Hi manufactured by Kyowa Interface Science Co., Ltd.) may be used.

$\begin{matrix} {{{\sqrt{\gamma_{H\; 2O}^{d}}\sqrt{\gamma^{d}}} + {\sqrt{\gamma_{H\; 2O}^{p}}\sqrt{\gamma^{p}}}} = \frac{\gamma_{H\; 2O}^{total}\left( {1 + {\cos \; \theta_{H\; 2O}}} \right)}{2}} & {\mspace{11mu} {({x1})}} \\ {{{\sqrt{\gamma_{{CH}\; 3I}^{d}}\sqrt{\gamma^{d}}} + {\sqrt{\gamma_{{CH}\; 3I}^{p}}\sqrt{\gamma^{p}}}} = \frac{\gamma_{{CH}\; 3I}^{total}\left( {1 + {\cos \; \theta_{{CH}\; 3I}}} \right)}{2}} & {({x2})} \\ {\gamma^{total} = {\gamma^{d} + \gamma^{p}}} & {(y)} \end{matrix}$

In Formulae (x1), (x2), and (y), γ^(d), γ^(p), and γ^(total) each denote the dispersion component, the polar component, and the sum of the dispersion component and the polar component of the surface free energy, respectively; γ_(H2O) and π_(CH3I) each denote the surface free energy of water and the surface free energy of diiodomethane, respectively; and θ_(H2O) and θ_(CH3I) each denote the contact angle of water and the contact angle of diiodomethane, respectively. The values of the surface free energy of water and diiodomethane are from a document (D. H. Kaelble, The Journal of Adhesion, 2, 2 (1970) 66.).

The arithmetic mean roughness, Ra, (indicative of the surface roughness) of the outer sole of the present invention is not particularly limited, but it is preferable that the arithmetic mean roughness, Ra, be 1000 μm or lower, more preferably from 5 μm to 100 μm, further preferably from 5 μm to 20 μm. With an arithmetic mean roughness, Ra, within this range, the outer sole has high levels of coefficients of static friction and dynamic friction on a road surface and, in particular, has an excellent grip performance. The arithmetic mean roughness, Ra, is the arithmetic mean roughness of the outer sole surface (which is one of the surfaces of the outer sole that comes into contact with a road surface), measured in accordance with JIS B0601-2001.

Examples of the method of obtaining the outer sole having an arithmetic mean roughness, Ra, within this range include (1) foaming the composition into a foam and (2) forming fine irregularities on the surface.

Provided that the outer sole contains the thermoplastic elastomer and has a surface free energy of 12 mJ/m² or higher, the composition may contain an additional component other than the thermoplastic elastomer. Examples of the additional component other than the thermoplastic elastomer include polymers other than the thermoplastic elastomer; and various additives, such as a foaming agent, a reinforcing agent, and a crosslinking agent.

The term “thermoplastic elastomer” herein refers to an elastomer that softens and becomes fluid upon heating and then returns to become rubber-like and elastic upon cooling.

The thermoplastic elastomer is not particularly limited, and examples thereof include a chlorinated polyethylene-based elastomer, a chlorosulfonated polyethylene-based elastomer, a polyester-based elastomer, a polyamide-based elastomer, a polystyrene-based elastomer, an olefin-based elastomer, a polyvinyl chloride elastomer, a urethane-based elastomer, a vinyl chloride-based elastomer, an acrylic-based elastomer, and a vinyl acetate-based elastomer. One of these may be used alone, or a combination of two or more of these may be used. It is preferable that the thermoplastic elastomer consist of at least one type of elastomer selected from a chlorinated polyethylene-based elastomer, a chlorosulfonated polyethylene-based elastomer, a styrene-based elastomer, an olefin-based elastomer, a polyamide-based elastomer, and a urethane-based elastomer.

Preferable examples of the thermoplastic elastomer include: (1) a chlorinated polyethylene-based elastomer alone, (2) a chlorosulfonated polyethylene-based elastomer alone, (3) at least a chlorinated polyethylene-based elastomer and an olefin-based elastomer, (4) a styrene-based elastomer alone, (5) a polyamide-based elastomer alone, (6) at least a styrene-based elastomer and a polyamide-based elastomer, (7) at least a styrene-based elastomer and a urethane-based elastomer, (8) at least a styrene-based elastomer and an olefin-based elastomer, (9) at least a styrene-based elastomer, an olefin-based elastomer, and a polyamide-based elastomer and/or a urethane-based elastomer, (10) at least a styrene-based elastomer and a polyamide-based elastomer, no olefin-based elastomer, (11) at least a styrene-based elastomer and a urethane-based elastomer, no olefin-based elastomer, and (12) at least a urethane-based elastomer. Hereinafter, a chlorinated polyethylene-based elastomer, a chlorosulfonated polyethylene-based elastomer, a styrene-based elastomer, an olefin-based elastomer, a polyamide-based elastomer, and a urethane-based elastomer are collectively called “first elastomers”, and thermoplastic elastomers other than the first elastomers are collectively called “second elastomers”.

The thermoplastic elastomer of the present invention consists of (a) at least one first elastomer, (b) at least one second elastomer, or (c) a combination of at least one first elastomer and at least one second elastomer. From the viewpoint to easily achieve a surface free energy of the outer sole of 12 mJ/m² or higher, it is preferable that the thermoplastic elastomer consists of at least a first elastomer, and it is more preferable that the first elastomer be at least one of a chlorinated polyethylene-based elastomer and a chlorosulfonated polyethylene-based elastomer.

The chlorinated polyethylene-based elastomer is a polymer in which some of or all of the hydrogen atoms of the polyethylene are substituted with chlorine atom(s). Provided that the chlorinated polyethylene-based elastomer contains a chloro group, a substituent or substituents other than chloro group may substitute the hydrogen atom or some of the hydrogen atoms of the polyethylene. The chlorinated polyethylene-based elastomer may be obtained by chlorinating a polyethylene powder or particle in an aqueous suspension or by chlorinating a polyethylene dissolved in an organic solvent, for example. The chlorine content in the chlorinated polyethylene-based elastomer ranges, for example, from 20% by mass to 50% by mass, preferably from 25% by mass to 45% by mass, in the whole chlorinated polyethylene. It is preferable that the chlorinated polyethylene-based elastomer be amorphous. Examples of the chlorinated polyethylene-based elastomer include a chlorinated ethylene homopolymer and a copolymer of chlorinated ethylene with an α-olefin (preferably, an α-olefin containing 12 or less carbon atoms). It is preferable that the copolymer contains the α-olefin in an amount of higher than 0% by mass and 10% by mass or lower in the whole chlorinated polyethylene, but it is not limited to the above-mentioned amount. The density of the chlorinated polyethylene-based elastomer is not particularly limited but ranges from 1.07 g/cm³ to 1.21 g/cm³, for example. The molecular weight of the chlorinated polyethylene-based elastomer is not particularly limited but ranges from 50,000 to 700,000, for example. The chlorinated polyethylene-based elastomer may be a crosslinked molecule or a non-crosslinked molecule.

As the chlorinated polyethylene-based elastomer, a commercially available product may be used. Examples of the commercially available product include “Elaslen” (trade name) manufactured by Showa Denko K.K.

A copolymer herein may be any of a random copolymer, a block copolymer, and a graft copolymer.

The chlorosulfonated polyethylene-based elastomer is a polymer in which the hydrogen atom or some of the hydrogen atoms of the polyethylene is substituted with a chlorosulfonyl group. Provided that the chlorosulfonated polyethylene-based elastomer contains a chlorosulfonyl group, a substituent or substituents other than chlorosulfonyl group may substitute some of the hydrogen atom or the hydrogen atoms of the polyethylene. The chlorosulfonated polyethylene-based elastomer may be obtained by chlorosulfonating a polyethylene with chlorine and sulfurous acid gas, for example. The chlorine content in the chlorosulfonated polyethylene-based elastomer ranges, for example, from 20% by mass to 50% by mass, preferably from 30% by mass to 40% by mass, in the whole chlorosulfonated polyethylene. It is preferable that the chlorosulfonated polyethylene-based elastomer be amorphous.

Examples of the chlorosulfonated polyethylene-based elastomer include a chlorosulfonated ethylene homopolymer and a copolymer of chlorosulfonated ethylene with an α-olefin (preferably, an α-olefin containing 12 or less carbon atoms). It is preferable that the content of the α-olefin in the copolymer be higher than 0% by mass and 10% by mass or lower in the whole chlorosulfonated polyethylene, but it is not limited to the above-mentioned content. The density of the chlorosulfonated polyethylene-based elastomer is not particularly limited but ranges from 1.10 g/cm³ to 1.40 g/cm³, for example. The chlorosulfonated polyethylene-based elastomer may be a crosslinked molecule or a non-crosslinked molecule.

As the chlorosulfonated polyethylene-based elastomer, a commercially available product may be used. Examples of the commercially available product include “TOSO-CSM TS-530” (trade name) manufactured by Tosoh Corporation and “Hypalon” (trade name) manufactured by DuPont Inc.

The polyester-based elastomer is a polymer containing an ester component. The polyester-based elastomer may be an ester homopolymer. It is preferable that the polyester-based elastomer be a copolymer composed of a polyester or a derivative thereof as its hard segment and a polyether or a polyester having a low glass transition temperature (Tg) as its soft segment. Specific examples of the polyester-based elastomer include a polyester-polyether copolymer composed of an aromatic crystalline polyester, such as polyethylene terephthalate or polybutylene terephthalate, as its hard segment and a polyether as its soft segment; and a polyester-polyester copolymer composed of an aromatic crystalline polyester as its hard segment and an aliphatic polyester as its soft segment.

The polyamide-based elastomer is a polymer containing a polyamide component. The polyamide-based elastomer may be an amide homopolymer or may be a copolymer of a polyamide component with another component. Examples of the copolymer include a copolymer composed of an aliphatic or aromatic polyamide or a derivative thereof as its hard segment and a component like a polyester or a polyether as its soft segment. Examples of the aliphatic or aromatic polyamide include nylon 6, nylon 64, nylon 66, nylon 610, nylon 612, nylon 46, nylon 9, nylon 11, nylon 12, N-alkoxymethyl-modified nylons, hexamethylenediamine-isophthalic acid condensation copolymer, and metaxyloyldiamine-adipic acid condensation copolymer.

The polystyrene-based elastomer is a polymer containing a styrene component. The polystyrene-based elastomer may be a styrene homopolymer. It is preferable that the polystyrene-based elastomer be a copolymer composed of a polystyrene or a derivative thereof as its hard segment and a component like butadiene as its soft segment.

The content of the hard segment in the polystyrene-based elastomer is not particularly limited. However, if the content of the hard segment is too low, the hard segment does not readily agglomerate, while if the content of the hard segment is too high, plasticity and elasticity of the polystyrene-based elastomer may be low. From these viewpoints, it is preferable that the content of the hard segment in the polystyrene-based elastomer ranges from 10% by mass to 65% by mass, more preferably from 20% by mass to 40% by mass, in the whole elastomer.

The polystyrene-based elastomer is not particularly limited and examples thereof include a styrene-butadiene block copolymer (abbreviated as SBR), a hydrogenated styrene-butadiene block copolymer (SEB), a styrene-butadiene-styrene block copolymer (SBS), a styrene-butadiene-butylene-styrene block copolymer (SBBS), a styrene-ethylene-butadiene-styrene block copolymer (SEBS), a styrene-isoprene block copolymer (SIR), a styrene-ethylene-propylene block copolymer (SEP), a styrene-isoprene-styrene block copolymer (SIS), a styrene-ethylene-propylene-styrene block copolymer (SEPS), a styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS), and a modified product of these.

The olefin-based elastomer is a polymer composed of a polyethylene and/or a polypropylene having rubber-like elasticity imparted thereto.

Typical examples of the olefin-based elastomer include a polypropylene-based elastomer and an α-olefin-based elastomer.

The polypropylene-based elastomer contains a polypropylene component, preferably contains a copolymer of a propylene with an ethylene. The polypropylene-based elastomer may be a propylene homopolymer or may be a copolymer of a polypropylene component with another component. Examples of the polypropylene-based elastomer include a polypropylene homopolymer and a propylene-ethylene random copolymer.

The α-olefin-based elastomer may be a copolymer of a polyethylene and/or a polypropylene with an α-olefin. The α-olefin is not particularly limited but it is preferable that the α-olefin be an α-olefin having 4 to 20 carbon atoms. The α-olefin may be a single type of α-olefin or may be a combination of two or more types of α-olefins. Examples of the α-olefin having 4 to 20 carbon atoms include 1-butene, isobutene, 1-pentene, 2-methyl-1-butene, 3-methyl-1-butene, 1-hexene, 2-methyl-1-pentene, 3-methyl-1-pentene, 4-methyl-1-pentene, 1-octene, 1-nonene, 1-decene, 1-undecene, and 1-dodecene. Among these, 1-butene, 1-hexene, and 1-octene are preferable.

Examples of the α-olefin-based elastomer include an ethylene-1-butene copolymer, a propylene-1-butene copolymer, an ethylene-1-hexene copolymer, a propylene-1-hexene copolymer, an ethylene-1-octene copolymer, and a propylene-1-octene copolymer. One of these may be used alone, or a combination of two or more of these may be used.

As the α-olefin-based elastomer, a commercially available product may be used. Examples of the commercially available product include “Tafmer” (trade name) manufactured by Mitsui Chemicals, Inc.

The urethane-based elastomer is a polymer containing a urethane component. The urethane-based elastomer may be a urethane homopolymer or may be a copolymer of a polyurethane component with another component. It is preferable that the urethane-based elastomer be a copolymer composed of a polyurethane or a derivative thereof as its hard segment and a component like a polyether or a polyester as its soft segment.

Examples of the urethane-based elastomer include a polyether-containing polyurethane and a polyester-containing polyurethane.

Examples of the vinyl chloride-based elastomer include a highly polymerized polyvinyl chloride elastomer, and a partially crosslinked polyvinyl chloride elastomer in which the crosslinked part functions as their hard segment and the linear part functions as their soft segment.

The acrylic-based elastomer is an acrylic-based polymer containing one, two, or more acrylic monomers.

As described above, the thermoplastic elastomer of the present invention may consist of (a) a first elastomer, (b) a second elastomer, or (c) a combination of a first elastomer and a second elastomer. In the case in which a combination of a first elastomer and a second elastomer is used, the second elastomer is appropriately selected from thermoplastic elastomers other than the following six types of thermoplastic elastomers: a chlorinated polyethylene-based elastomer, a chlorosulfonated polyethylene-based elastomer, a styrene-based elastomer, an olefin-based elastomer, a polyamide-based elastomer, and a urethane-based elastomer.

In the case in which the thermoplastic elastomer consists of a combination of a first elastomer and a second elastomer, the ratio between the first elastomer and the second elastomer is not particularly limited. It is preferable for the mass ratio (first elastomer):(second elastomer) to range from 100:0 to 60:40, more preferably from 85:15 to 65:35 because with this mass ratio, it is easy to regulate the surface free energy to 12 mJ/m² or higher. The mass ratio (first elastomer): (second elastomer) of 100:0 mentioned above corresponds to a case in which the thermoplastic elastomer consists solely of a first elastomer, which does not fit the description “the thermoplastic elastomer consists of a combination of a first elastomer and a second elastomer”. Despite that, the expression “the mass ratio (first elastomer): (second elastomer) ranging from 100:0 to 60:40” is employed above for describing the ratio between both elastomers.

Examples of the additional polymers other than the thermoplastic elastomer include rubbers.

The rubbers are not particularly limited and examples thereof include synthetic rubbers such as butadiene rubber (BR), isoprene rubber (IR), and chloroprene (CR); natural rubber (NR); and copolymer rubbers such as styrene-butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR), and butyl rubber (IIR). One of these rubbers may be used alone, or a combination of two or more of these may be used.

In the case in which one or more of the additional polymers other than the thermoplastic elastomer are used, the content thereof is not particularly limited provided that the resulting outer sole has a surface free energy of 12 mJ/m² or higher. The content of the additional polymers other than the thermoplastic elastomer may be higher than 0 part by mass and 500 parts by mass or lower, preferably higher than 0 part by mass and 400 parts by mass or lower, relative to 100 parts by mass of the thermoplastic elastomer.

To produce a foamed article, chemical foaming is typically employed, which requires use of a suitable foaming agent.

The foaming agent is used in the case in which the outer sole of the present invention is made into a foamed article. Use of the foaming agent is required in chemical foaming for foaming the composition. In the case in which physical foaming is employed for foaming the composition into a foamed article, use of the foaming agent may not be required.

Examples of the foaming agent include sodium hydrogen carbonate, ammonium bicarbonate, sodium carbonate, ammonium carbonate, azodicarbonamide (ADCA), dinitrosopentamethylenetetramine (DNPT), azobisisobutyronitrile, barium azodicarboxylate, and p,p′-oxybisbenzenesulfonyl hydrazine (OBSH).

For facilitating foaming, a foaming aid may be concurrently used with the foaming agent. Examples of the foaming aid include zinc oxide, urea, and urea derivatives.

The content of the foaming agent is not particularly limited and is appropriately determined. For example, the content of the foaming agent ranges from 0.5 parts by mass to 5 parts by mass relative to 100 parts by mass of the thermoplastic elastomer.

The reinforcing agent is not particularly limited and may be a conventionally known reinforcing agent.

Examples of the reinforcing agent include silica, carbon black, activated calcium carbonate, and magnesium silicate ultrafine particles.

It is preferable that the reinforcing agent is hydrous silica (white carbon), which can give a low-foamed outer sole having a relatively low density, an excellent mechanical strength, and an excellent abrasion resistance.

The content of the reinforcing agent is not particularly limited and is appropriately determined. For example, the content of the reinforcing agent ranges from 10 parts by mass to 40 parts by mass relative to 100 parts by mass of the thermoplastic elastomer.

The crosslinking agent is not particularly limited and may be a conventionally known crosslinking agent.

Examples of the crosslinking agent include a sulfur-containing compound and an organic peroxide. Examples of the sulfur-containing compound include sulfur, sulfur halides, di-2-benzothiazolyl disulfide, and N-oxydiethylene-2-benzothiazolylsulfenamide. Examples of the organic peroxide include dicumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and 1,1-di(t-butylperoxy)cyclohexane. By using the crosslinking agent, the thermoplastic elastomer undergoes crosslinking and thereby the resulting outer sole has an excellent elasticity. Alternatively, the outer sole of the present invention may be produced by using a composition containing no crosslinking agent.

For facilitating crosslinking of the thermoplastic elastomer, a crosslinking promoter may be concurrently used with the crosslinking agent.

The content of the crosslinking agent is not particularly limited and is appropriately determined. For example, the content of the crosslinking agent ranges from 0.1 parts by mass to 5 parts by mass, preferably from 0.3 parts by mass to 3 parts by mass, relative to 100 parts by mass of the thermoplastic elastomer.

The composition used for producing the outer sole of the present invention may contain other additives, such as a heat stabilizer, a light stabilizer, an antioxidant, an ultraviolet absorber, a colorant, a plasticizer, an antistatic agent, a thickener, a processed oil, and stearic acid.

[Production of Outer Sole]

The composition is shaped into the sole of a shoe.

Specific procedures are as follows. The composition is prepared by mixing the thermoplastic elastomer, and optionally one or more of the additional polymers other than the thermoplastic elastomer, and various additives such as the crosslinking agent, each in a certain amount. The resulting composition is kneaded in a mixing roll, a pressure kneader, or an extruder, for example, while being heated to a temperature ranging from 70° C. to 150° C.

After thorough kneading, the resulting composition is poured into a press mold, followed by, for example, pressing for a certain period of time while being heated to a temperature ranging from 150° C. to 200° C. Thus, an outer sole can be obtained. Alternatively, after thorough kneading, the resulting composition is transferred into an injection molding machine for injection molding, and thereby an outer sole can be obtained.

In the case in which the composition is hot-pressed by using a press mold having an outer-sole shape, the resulting primary molded article may be used as it is as the outer sole. Alternatively, the primary molded article obtained by hot-pressing the composition may be subjected to secondary processing and the resulting product may be used as the outer sole of the present invention.

The outer sole may be a foamed article produced by foaming the composition, or may be a non-foamed article produced from the composition without foaming. By foaming the composition, the outer sole having the above-described arithmetic mean roughness, Ra, can be easily obtained. From the view points of a high arithmetic mean roughness and excellent cushioning effect, it is preferable that the outer sole of the present invention be a foamed article.

In the case in which the composition is subjected to foaming, the foaming ratio is not particularly limited but ranges from 1.05 to 1.4, for example, preferably from 1.05 to 1.2.

The density of the outer sole is not particularly limited. From the viewpoint of weight reduction, it is preferable that the density of the outer sole be 0.6 g/cm³ or lower, more preferably 0.55 g/cm³ or lower, further preferably 0.5 g/cm³ or lower. It is preferable that the lower limit to the density of the outer sole be as low as possible, typically 0.2 g/cm³ or higher, preferably 0.3 g/cm³ or higher. The density is measured in accordance with JIS Z 8807.

[Applications of Outer Sole of Present Invention]

The outer sole of the present invention is used as the outer sole of a shoe, attached to the bottom side of the body of the shoe, for example.

The outer sole of the present invention is attached to the entire area of the bottom side of the shoe body. Alternatively, the outer sole of the present invention may be attached to a partial area of the bottom side of the shoe body.

The outer sole of the present invention may also be used as a reinforcing component, such as a shank component, of a shoe. The shank component is a bottom-forming component, disposed in the area of a shoe that comes under the arch of a foot of the shoe's wearer.

The shape of the outer sole may be any shape. For example, the outer sole may be substantially platy, or may be substantially convex (like the outer soles of a pair of spikes with many circular truncated points). The bottom side of the outer sole may be smooth, but it typically has irregularities in any appropriate form. The bottom side of the outer sole herein refers to the side of the outer sole opposite to the upper side of the outer sole, that is, opposite to the side of the outer sole that is to be attached to the bottom side of the shoe body.

The outer sole is fixed to the shoe body with an adhesive, for example.

The adhesive is not particularly limited and examples thereof include conventionally known adhesives, such as solvent adhesives, emulsion adhesives, laser adhesives, and thermal adhesives. The solvent adhesives are a type of adhesives containing a binder resin dissolved or dispersed in an organic solvent. The emulsion adhesives are a type of adhesives containing a binder resin dispersed in water. The laser adhesives are a type of adhesives that exhibits its adhesive ability upon laser irradiation. The thermal adhesives are a type of adhesives that exhibits its adhesive ability upon heating.

[Configuration and Applications of Shoe of Present Invention]

FIGS. 1 and 2 both illustrate a first embodiment of the shoe of the present invention.

A shoe 1 a includes a shoe body 2 a, a midsole 3 a attached to the bottom side of the shoe body 2 a, and an outer sole 5 a attached to the bottom side of the midsole 3 a. The shape of the midsole 3 a is substantially the same as that of the bottom side of the shoe body 2 a. The shape of the outer sole 5 a is substantially the same as that of the bottom side of the midsole 3 a. The outer sole 5 a is substantially platy. The bottom side of the platy outer sole 5 a has irregularities as intended, as shown in FIG. 2. Alternatively, the bottom side of the outer sole 5 a may be smooth (not illustrated).

The upper side of the midsole 3 a is bonded to the bottom side of the shoe body 2 a with an adhesive, and the upper side of the outer sole 5 a is bonded to the bottom side of the midsole 3 a with an adhesive (the adhesive is not illustrated). In the case of using this shoe 1 a, the bottom side of the outer sole 5 a comes into contact with the ground. The outer sole of the present invention may be used as the outer sole 5 a of the shoe 1 a, or as the midsole 3 a of the shoe 1 a, or as each of the midsole 3 a and the outer sole 5 a of the shoe 1 a.

FIG. 3 illustrates a second embodiment of the shoe of the present invention.

A shoe 1 b includes a shoe body 2 b, a midsole 3 b attached to the bottom side of the shoe body 2 b, a first outer sole 51 b attached to the front part of the bottom side of the midsole 3 b, and a second outer sole 52 b attached to the rear part of the bottom side of the midsole 3 b. The shape of the midsole 3 b is substantially the same as that of the bottom side of the shoe body 2 b. Each of the first outer sole 51 b and the second outer sole 52 b is smaller than the bottom side of the midsole 3 b.

The upper side of the midsole 3 b is bonded to the bottom side of the shoe body 2 b with an adhesive, and the upper sides of both the first outer sole 51 b and the second outer sole 52 b are bonded to the bottom side of the midsole 3 b with an adhesive (the adhesive is not illustrated). In the case of using this shoe 1 b, the bottom sides of both the first outer sole 51 b and the second outer sole 52 b come into contact with the ground and a partial area of the bottom side of the midsole 3 b may also come into contact with the ground.

The outer sole of the present invention may be used as the first outer sole 51 b and/or the second outer sole 52 b of the shoe 1 b.

The thickness of each of the midsole 3 a and the midsole 3 b is not particularly limited. For providing the resulting shoe with an appropriate degree of cushioning, the thickness of each of the midsole 3 a and the midsole 3 b is 2 mm or more, for example, preferably from 2 mm to 10 mm.

The thickness of each of the outer sole 5 a, the first outer sole 51 b, and the second outer sole 52 b is not particularly limited. For providing the resulting shoe with an appropriate degree of cushioning, the thickness of each of the outer sole 5 a, the first outer sole 51 b, and the second outer sole 52 b is 2 mm or more, for example, preferably from 2 mm to 20 mm.

Regarding the configuration of the shoe of the present invention, the shoe body may protect substantially the entire instep, as illustrated in the figure, or may protect only a part of the instep (like a sandal).

The shoe of the present invention is not particularly limited in its applications. The shoe of the present invention may be used as a shoe for various ball sports, such as a soccer shoe or a rugby shoe; a running shoe, such as a jogging shoe or a marathon shoe; a shoe for track and field; a shoe for sports in general; a walking shoe; a flip flop; and the like.

The outer sole of the present invention has an excellent grip performance on a road surface. The outer sole of the present invention also has an excellent grip performance on a wet road surface, particularly on a wet, smooth road surface.

The shoe of the present invention having this outer sole is suitable for use as a shoe for ball sports, a running shoe, a shoe for track and field, and a walking shoe.

EXAMPLES

The present invention will be described in further detail referring to examples and comparative examples. The scope of the present invention is not limited to these examples.

In the [Composition] rows in Tables 1 to 3, the numerical values are in part(s) by mass.

[Materials Used in Examples and Comparative Examples]

Chlorinated polyethylene-based elastomer: “Elaslen 301A” (trade name) manufactured by Showa Denko K.K., chlorine content=about 30% by mass.

α-Olefin-based elastomer: “Tafmer DF810” (trade name) manufactured by Mitsui Chemicals, Inc., copolymer of ethylene and 1-butene.

Styrene-based elastomer (1): “Septon V9461” (trade name) manufactured by KURARAY CO., LTD., styrene-ethylene-ethylene-propylene-styrene block copolymer (abbreviated as SEEPS).

Styrene-based elastomer (2): “M1913” (trade name) manufactured by Asahi Kasei Chemicals Corporation, styrene-ethylene-butadiene-styrene block copolymer modified with maleic acid (abbreviated as MA-modified SEBS).

Polyamide-based elastomer (1): “1010C1” (trade name) manufactured by DSM, nylon 6 homopolymer.

Polyamide-based elastomer (2): “3010SR” (trade name) manufactured by DSM, nylon 66 homopolymer.

Urethane-based elastomer: “ET195” (trade name) manufactured by BASF, copolymer composed of a polyurethane as its hard segment and a polyester as its soft segment.

Chlorosulfonated polyethylene-based elastomer: “TS-530” (trade name) manufactured by Tosoh Corporation, chlorine content=about 35% by mass.

Polypropylene-based elastomer: “E-105-GM” (trade name) manufactured by Prime Polymer Co., Ltd.

Isoprene rubber: “IR2200” (trade name) manufactured by Zeon Corporation.

Oil (1): processed oil, “PW90” (trade name) manufactured by Idemitsu Kosan Co., Ltd.

Oil (2): processed oil, “DOZ” (trade name) manufactured by New Japan Chemical Co., Ltd.

Oil (3): processed oil, “P200” (trade name) manufactured by JX Nippon Oil & Energy Corporation.

Crosslinking agent (1): dicumyl peroxide, “Percumyl D” (trade name) manufactured by Nippon Oil & Fats Co., Ltd.

Crosslinking agent (2): 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, “Perhexa 25B-40” (trade name) manufactured by Nippon Oil & Fats Co., Ltd.

Crosslinking agent (3): sulfur, “sulfur #200” (trade name) manufactured by Hosoi Chemical Industry Co., Ltd.

Crosslinking aid (1): triallyl isocyanurate, “TAIC M-60” (trade name) manufactured by Nippon Kasei Chemical Company Limited.

Crosslinking aid (2): trimethylolpropane trimethacrylate, “SR350” (trade name) manufactured by Sartomer.

Crosslinking aid (3): “Nocceler” (trade name) manufactured by Ouchi Shinko Chemical Industrial Co., Ltd.

Foaming agent: azodicarbonamide, “Vinyfor AC#3C-K2” (trade name) manufactured by Eiwa Chemical Ind. Co., Ltd.

Foaming aid: zinc oxide, “Activated Zinc White No. 2” (trade name) manufactured by The Honjo Chemical Corporation.

Silica: “VN3” (trade name) manufactured by Degussa Japan.

Silane coupling agent: “Si-69” (trade name) manufactured by Degussa Japan.

Stearic acid: “Stearic Acid 505” (trade name) manufactured by New Japan Chemical Co., Ltd.

Zinc oxide: “Activated Zinc White No. 2” (trade name) manufactured by The Honjo Chemical Corporation.

Example 1

Materials listed in the [Material] section above were mixed according to the proportion specified in Table 1. The resulting composition of these materials was kneaded in a pressure kneader and a mixing roll and then poured into a press mold having a size of 150 mm in length, 150 mm in width, and 5.5 mm in thickness, followed by pressing at an oil pressure ranging from 130 kgf/cm² to 150 kgf/cm² for 20 minutes while heating to 160° C. In this way, a rectangular foamed article having a size of about 170 mm in length, about 170 mm in width, and about 10 mm in thickness was prepared (the foaming ratio was about 1.1).

TABLE 1 Comparative Example 1 Example 2 Example 3 Example 4 Example 5 Example 1 Compo- Chlorinated 100 80 60 40 20 sition polyethylene- based elastomer α-olefin-based 20 40 60 80 100 elastomer Crosslinking 0.5 0.5 0.5 0.5 0.5 0.5 agent (1) Crosslinking 0.25 0.25 0.25 0.25 0.25 0.25 aid (1) Foaming agent 1 1 1 1 1 1 Foaming aid 3 3 3 3 3 3 Total 104.75 104.75 104.75 104.75 104.75 104.75 Surface free energy 17.2 15.7 15.5 15.8 12.4 9.8 (mJ/m²) Surface roughness Ra 19.02 10.28 12.75 8.05 9.13 16.97 (μm) Coefficient of 0.654 0.552 0.530 0.487 0.470 0.358 static friction Coefficient of 0.452 0.447 0.439 0.438 0.426 0.306 dynamic friction

Examples 2 to 5 and Comparative Example 1

In the same manner as in Example 1 and by using materials according to the proportion specified in Table 1, a composition was prepared and a foamed article was produced from the resulting composition.

Examples 6 to 12

Materials listed in the [Material] section were mixed according to the proportion specified in Table 2. The resulting composition of these materials was fed into a twin screw extruder, where the composition was kneaded for dynamic crosslinking while being heated to a temperature ranging from 230° C. to 270° C. The kneaded product was fed into an injection molding machine and was then ejected into a mold while being heated to a temperature ranging from 230° C. to 270° C. In this way, a rectangular non-foamed article having a size of about 110 mm in length, about 50 mm in width, and about 2 mm in thickness was prepared.

TABLE 2 Example 6 Example 7 Example 8 Example 9 Example 10 Example 11 Example 12 Compo- Styrene-based 46.67 46.67 50.00 46.67 50.00 46.67 50.00 sition elastomer (1) Styrene-based 20.00 20.00 21.43 20.00 21.43 20.00 21.43 elastomer (2) Polyamide-based 20.00 28.57 elastomer (1) Polyamide-based 20.00 28.57 elastomer (2) Urethane-based 20.00 28.57 elastomer Polypropylene- 33.33 13.33 13.33 13.33 based elastomer Oil (1) 66.67 66.67 71.43 66.67 71.43 66.67 71.43 Crosslinking 1.33 1.33 1.43 1.33 1.43 1.33 1.43 agent (2) Crosslinking 6.67 6.67 7.14 6.67 7.14 6.67 7.14 aid (2) Total 174.67 174.67 180.00 174.67 180.00 174.67 180.00 Surface free energy 27.5 30.5 47.1 30.1 44.0 35.4 37.0 (mJ/m²) Surface roughness Ra 0.49 0.56 0.78 0.65 1.01 0.49 0.65 (μm) Coefficient of 0.921 1.017 1.458 1.145 1.281 1.102 1.113 static friction Coefficient of 0.358 0.447 1.039 0.509 0.962 0.621 0.805 dynamic friction

Example 13

Materials listed in the [Material] section were mixed according to the proportion specified in Table 3. The resulting composition of these materials was kneaded in a pressure kneader and a mixing roll and then poured into a press mold having a size of 125 mm in length, 215 mm in width, and 2 mm in thickness, followed by pressing at an oil pressure ranging from 130 kgf/cm² to 150 kgf/cm² for 5 minutes while heating to 160° C. In this way, a rectangular non-foamed article having a size of about 125 mm in length, about 215 mm in width, and about 2 mm in thickness was prepared.

Examples 14 and 15

Materials listed in the [Material] section were mixed according to the proportion specified in Table 3. The resulting composition of these materials was kneaded in a pressure kneader and a mixing roll and then poured into a press mold having a size of 125 mm in length, 215 mm in width, and 2 mm in thickness, followed by pressing at an oil pressure ranging from 130 kgf/cm² to 150 kgf/cm² for 30 minutes while heating to 160° C. In this way, a rectangular non-foamed article having a size of about 125 mm in length, about 215 mm in width, and about 2 mm in thickness was prepared.

Comparative Example 2

Materials listed in the [Material] section were mixed according to the proportion specified in Table 3. The resulting composition of these materials was kneaded in a pressure kneader and a mixing roll and then poured into a press mold having a size of 125 mm in length, 215 mm in width, and 2 mm in thickness, followed by pressing at an oil pressure ranging from 130 kgf/cm² to 150 kgf/cm² for 20 minutes while heating to 160° C. In this way, a rectangular non-foamed article having a size of about 125 mm in length, about 215 mm in width, and 2 mm in thickness was prepared.

TABLE 3 Compar- ative Example Example Example Example 13 14 15 2 Comp- Chlorinated 100 20 sition polyethylene- based elastomer Chlorosulfonated 100 polyethylene- based elastomer Isoprene rubber 80 100 Oil (2) 10 10 Oil (3) 20 Crosslinking 2.0 2.0 agent (3) Crosslinking 2.3 2.3 4.0 aid (3) Silica 20 20 45 Silane coupling 4.5 agent Stearic acid 2 Zinc oxide 5 Other additives 12 12 3 Total 100.0 144.3 146.3 185.5 Surface free energy 29.4 29.9 24.3 19.0 (mJ/m²) Surface roughness Ra 0.51 0.21 0.62 0.3 (μm) Coefficient of 0.601 1.043 1.073 0.406 static friction Coefficient of 0.397 0.493 0.448 0.351 dynamic friction

[Surface Free Energy of Compositions in Examples and Comparative Examples]

On the outer sole surface, 1 μL of ion-exchanged water was dropped, and 10 seconds later, the contact angle was measured. In the same manner, 1 μL of diiodomethane was dropped on the outer sole surface, and 10 seconds later, the contact angle was measured. The values of the contact angles were substituted into the simultaneous equations of Formulae (x1) and (x2) to solve these equations. The solutions, γ^(d) and γ^(p), were substituted into Formula (y). Thus, the value of the surface free energy of the outer sole was determined.

As the diiodomethane, a Wako 1st Grade reagent manufactured by Wako Pure Chemical Industries, Ltd. was used. As the device for contact angle measurement, a contact angle meter (DM-510Hi manufactured by Kyowa Interface Science Co., Ltd.) was used. γ_(H2O) and γ_(CH3I) in Formulae (x1) and (x2) (the values of the surface free energy of water and diiodomethane) were obtained from a document (D. H. Kaelble, The Journal of Adhesion, 2, 2 (1970) 66.).

[Arithmetic Mean Roughness, Ra, in Examples and Comparative Examples]

The arithmetic mean roughness, Ra, of each of the foamed articles and the non-foamed articles (for use as an outer sole) prepared in the examples and the comparative examples was measured in accordance with JIS B0601-2001. More specifically, the surface roughness (the arithmetic mean roughness) of each of these was measured with a One-shot 3D Measuring Macroscope VR-3000 manufactured by Keyence Corporation. The results are shown in Tables 1 to 3.

[Coefficients of Static Friction and Dynamic Friction in Examples and Comparative Examples]

The coefficients of static friction and dynamic friction of the foamed articles and the non-foamed articles (for use as an outer sole) prepared in the examples and the comparative examples were measured in accordance with JIS T8101.

More specifically, each of the foamed articles and the non-foamed articles prepared in the examples and the comparative examples was fixed to the bottom of a safety shoe that had no outer sole. The resulting safety shoe was placed on a stainless steel surface that was wet with water. Then, the safety shoe was made to slide at a sliding rate of 0.22 m/second with a vertical load of 500 N being applied, while the coefficients of static friction and dynamic friction were being measured. The results are shown in Tables 1 to 3.

In addition to these tables, FIG. 4 provides a graph showing the results of the coefficient of static friction and the coefficient of dynamic friction obtained in Examples 1 to 5 and Comparative Example 1.

EVALUATION

Referring to Table 1 and FIG. 4, it has been proven that each of the outer soles in Examples 1 to 5 has high coefficients of static friction and dynamic friction on a road surface compared to Comparative Example 1. Especially, an increase in the content of the chlorinated polyethylene-based elastomer has contributed to a remarkable increase in the coefficient of static friction. Evaluation was conducted as follows: the higher the coefficient of friction was, the more slip resistant the outer sole was.

Under the conditions in which a shoe is used, the coefficient of static friction of the outer sole refers to the friction on a road surface at the time when the shoe's movement is started, and the coefficient of dynamic friction of the outer sole refers to the friction on a road surface at the time when the shoe's movement is stopped. The time when the shoe's movement is started refers to, for example, the time when the wearer starts to run or walk, and the time when the shoe's movement is stopped refers to, for example, the time when the wearer changes the direction to proceed while running.

Referring to Table 2, it has been proven that each of the outer soles in Examples 6 to 12 has high coefficients of static friction and dynamic friction on a road surface. In particular, the coefficients of dynamic friction in Examples 8, 10, and 12 where no polypropylene-based elastomer is used are remarkably higher than those in Examples 6, 7, 9, and 11 where a polyolefin-based elastomer is used. The coefficients of static friction in Examples 7 to 12 where a polyamide-based elastomer or a urethane-based elastomer is used are higher than that of Example 6 where no polyamide-based elastomer nor urethane-based elastomer is used. From a comparison between Example 7 and Example 8 and a comparison between Example 9 and Example 10, it has been proven that an outer sole having a higher content of polyamide-based elastomer has a higher surface free energy.

Referring to Table 3, it has been proven that each of the outer soles in Examples 13 to 15 has higher coefficients of static friction and dynamic friction on a road surface than those in Comparative Example 2.

In Comparative Example 2, the surface free energy was 19.0 mJ/m² but the absence of a thermoplastic elastomer resulted in low coefficients of static friction and dynamic friction.

INDUSTRIAL APPLICABILITY

An outer sole of the present invention can be used as a structural element of a shoe.

-   1 a, 1 b Shoe -   2 a, 2 b Shoe body -   3 a, 3 b Midsole -   5 a, 51 b, 52 b Outer sole 

1. An outer sole, comprising a thermoplastic elastomer and having a surface free energy of 12 mJ/m² or higher across an entire surface of the outer sole.
 2. The outer sole according to claim 1, having an arithmetic mean roughness, Ra, of 1000 μm or lower.
 3. The outer sole according to claim 1, wherein the thermoplastic elastomer contains at least one elastomer selected from a chlorinated polyethylene-based elastomer, a chlorosulfonated polyethylene-based elastomer, a styrene-based elastomer, an olefin-based elastomer, a polyamide-based elastomer, and a urethane-based elastomer.
 4. The outer sole according to claim 1, wherein the thermoplastic elastomer contains at least one of a chlorinated polyethylene-based elastomer and a chlorosulfonated polyethylene-based elastomer.
 5. A shoe, comprising the outer sole according to claim
 1. 